Over at least the last 10 years, considerable attention has been directed to mooring systems employing composite mooring lines. This has been due largely, though not exclusively, to growing use of offshore drill platforms which must often be moored in very deep water during oil exploration. The advantages of employing a composite mooring line consisting of a lower length of chain cable serially connected to an upper length of wire rope are well recognized. In particular better anchoring characteristics at certain water depths can be achieved than is possible through use of wire rope or chain alone. An overall capability to moor in deeper water is obtained. However, use of a composite mooring line introduces new problems, including problems of conveying a chain cable-wire rope connector over fairlead sheaves and the like, and both increased demand on deck space and greater system weight because of the requirement for both winches and windlasses to handle the composite mooring line.
First mooring systems adapted to handle composite mooring lines involved a breaking and re-making of the chain cable-wire rope connection during hauling in and paying out. Basically, the components of the mooring line were separated, depending on whether chain cable was to be conveyed by a windlass or wire rope by a winch. In particular, U.S. Pat. No. 3,842,776 issued to Wudtke on Oct. 22, 1974 introduced a particular disconnect system which included a special wire rope-chain cable connector carried by an outermost groove of the system fairlead sheave during transition from wire rope to chain cable avoiding undue bending of the wire rope during such transition.
An alternative non-disconnect system was proposed in U.S. Pat. No. 3,912,228 which issued to Petty et al on Oct. 14, 1975. That mooring system involves a windlass and drum winch, and a sheave positioned in the interior of an associated chain locker a sufficient distance below the winch that acceptable fleet angles are maintained, and in an orientation which permits the chain to be deposited inside the chain locker without disengaging the mooring line from the interior sheave. During hauling in, for example, the wire rope can be hauled in by the winch until links of chain cable deposit in pockets of the chain wheel, and the chain wheel then actuated to deposit the chain cable into a locker positioned below the chain wheel.
In U.S. Pat. No. 4,476,801 issued on Oct. 16, 1984 to Foster and Rich, there is described a more recently developed non-disconnect system in which a traction winch is mounted vertically over a windlass to achieve a common line of action for both chain and wire rope. A retractor is provided to draw chain from the vertical line of action over the chain wheel to engage the chain links with the whelps of the chain wheel so that the chain may be deposited into a chain locker. Advantageously, such a system eliminates the problem of conveying a wire rope-chain cable connector over the windlass chain wheel.
Such mooring systems have obviated the disconnection problem; however, they still involve a separate winch and windlass, each designed, together with associated brake mechanisms, to handle individually the maximum loads expected on the mooring line.
Accordingly, it is an object of the present invention to more fully integrate the winch and windlass functions of a mooring system adapted to handle a composite mooring line.